In air-drying systems, where a continuous supply of air is critical, it has been the practice to have an emergency standby air-drying back-up system capable of taking over the full demand for dry air in the event of a failure of the primary system. In the prior art, the standby unit has required time after starting in which to reach full capability for dry air delivery. This lag has resulted in loss of dry air for a time at the point of use. The primary dry air supply system and the emergency standby system each comprise a complete system with its compressor, air-dryer, valves, regulators and alarm sensors for detecting increase in humidity or other conditions indicating changes from the desired operating conditions for the system, and the primary system and standby system are each capable of supplying the full demand for dry air or other gas to a place of use when the other system is not in operation and for indefinite periods of time such as a day or a plurality of successive days.
Where a standby system has remained idle for a substantial length of time, certain parts of the system may not remain in condition for instant operation; for example, a drying system having an adsorptive air dryer requires sufficient quantity of air to maintain positive regeneration flow on the adsorptive air dryer to prevent wetting of the adsorbent due to breathing atmospheric air or other moisture sources during extended standby periods.
This invention keeps the standby unit in condition for instant operation by maintaining any dynamic conditions necessary to keep the standby unit in an active or ready condition.
This result is accomplished by bleeding some of the dry air from the operating primary system into parts of the idle back-up system. The quantity of air supplied depends on the type of drying system used in the back-up system. In addition to the adsorptive air dryer, mentioned above, a standby system with a refrigerator dryer must be supplied with a flow sufficient to prevent extreme low temperatures that would cause frosting or freeze-up of the heat exchanger to an extent which would require considerable operation of the back-up system before it would be operating normally.
Other examples of maintaining dynamic conditions in the standby system include the supplying of sufficient air to maintain proper pressure swing development for a heaterless adsorptive drying system; and a flow sufficient to maintain all of the dry air delivery circuits of the standby unit in a low humidity condition. The compressor of the standby unit is deactivated while the parts of the standby or back-up unit are maintained in the necessary dynamic conditions for instant use by the dry air which is bled off from the primary air-drying system to parts of the standby system.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.